The majority of inks and toners used in the printing industry employ water insoluble polymers for print adhesion and durability. Water-based inks, such as used in ink-jet printing, can incorporate water insoluble polymers as dispersed particulates. The particulates are typically designed to allow formation of a print-film on the printed substrate. Alternatively, these water insoluble polymers can be coated on the surface of pigments in the form of polymer-encapsulated pigments.
Polymer encapsulated pigments of various kinds are known in the colorant art. The Sunsperse® and Flexiverse® polymer coated pigments from Sun Chemical Corp. are representative. While some encapsulation methods and chemistries are known, ink-jet inks including such polymer encapsulated pigments often do not perform well in thermal ink-jet architecture. One prevalent method involves capsules formed typically with dissolved polymers that are adsorbed onto the pigment surface. Inasmuch as the dissolved polymers are usually not crosslinked, the polymer surfaces of such known encapsulated pigments typically agglomerate under the high thermal shear and solvent conditions of the pen firing chamber, causing nozzle and ink channel blockages. Thus, typically, the incorporation of such polymer encapsulated pigments within thermal ink-jet inks typically results in poor pen reliability.
Conversely, the introduction of separate pigment and polymer particle components has several shortcomings as well. The combined surface areas of the latex and pigment particles adversely modify the viscosity of the ink-jet such that drop ejection rates are limited to lower than otherwise norms. Such viscosities also negatively impact the collapse of nucleated vapor bubbles on thermal drop ejection, entrapping gas within firing chamber upon subsequent firings. Entrapped gas significantly retards ink-jettability. Likewise, differences between latex and pigment surface charges and charge levels can induce dispersion instabilities and performance changes within the ink over time. In addition, the pigment and latex often dissociate in the fibers of plain paper reducing both the otherwise durability and optical density of the print. Still further, many entrapped pigment particles are exposed above the surface of the latex film, lowering print gloss and inducing gloss non-uniformities between different colored pigments within a print.
Thus, there is a continued need for development of pigment- and polymeric material-containing ink-jettable inks that are reliable when using thermal ink-jet architecture.